Even a year after its release, the Radeon HD 4870 X2 sits unchallenged as ATi's flagship graphics solution, but at more than £240 it is priced beyond the reaches of many PC enthusiasts. The HD 4850 X2 from Sapphire shares much of the same technology with that card but costs a considerably more palatable £170 including VAT.

The RV770 GPUs are identical in both models, though in this variant they are clocked 125MHz slower. The memory is considerably less snappy as well, as it runs at 1986MHz compared to the rip-roaring 3600MHz of the flagship. Arguably the most important difference between the two is the memory count, as with just 1GB of memory to share between its two GPUs this card has half of the 4870 X2's allocation. This turned out to be a remarkably performance-limiting factor in a number of our benchmarks.

Aesthetically, the Sapphire HD 4850 X2 looks the part, with a smart black shroud covering a substantial aluminium slab beneath. In turn, this heat sink is cooled by a pair of large 80mm fans that blow cool air directly over each GPU. Although a new BIOS from Sapphire has calmed these fans notably from the helicopter-like din they produced in early revisions of this card, they will still be noticeable over most CPU coolers and rev up to even louder speeds when taxed.

Get the latest Dell Coupons and other computer coupons at CheapStingyBargains.com.

Another downside to the cooling system is that it dumps heat straight back into the PC case rather than exhausting it out of the back as many other high-end cards do. This compromise is necessitated by Sapphire's decision to provide no fewer than four DVI ports. This makes the 4850 X2 the first mainstream card we have tested capable of powering four monitors. Whilst this won't be of interest to most gamers, it certainly makes the card an interesting proposition for traders and other professionals who require expansive screen real-estate.

Having a high end dual-GPU video card is all about being able to run games at the highest levels of detail. We therefore tested the card on a 24-inch monitor at 1920 x 1200 and maxed out each of our test game's detail settings. In Crysis Warhead, the HD 4850 X2 managed a rather feeble 9.8fps average compared to the much more impressive 27fps and 33fps of the 4870 X2 and GeForce GTX 295 respectively. This trend was continued in Call of Duty: World at War, where Sapphire's card recorded an occasionally jerky 45fps compared to the silky smooth 114fps and 132fps of the competition.

Although we were expecting the 4850 X2 to be slower than these two more expensive solutions, it is clearly the small memory allocation that is holding back the card's performance rather than the actual architecture. At the highest detail levels with FSAA and Anisotropic Filtering enabled, video card memory is at a premium; especially in games with lots of high resolution textures like these two particular A-list titles.

In other, less-demanding games the card was not so hobbled. Even with every setting maxed out the 4850 X2 managed an impressive 42fps in FarCry 2 and an equally adept 43fps in HawX. Zombie FPS Left 4 Dead was also dispatched with ease, with the Sapphire demonstrating an impressive 66fps average frame rate with every slider set to maximum. The limited memory count once again came back to bite us in Grand Theft Auto IV, however, where we were unable to set the sliders beyond medium settings at 1920x1200.

In order to properly run the HD 4850 X2 you will need an extremely well-cooled case and a very beefy PSU. We'd recommend at least a 600W unit, and you'll need two PCI Express power cables; one with eight pins and one with the standard six. As you'd expect for a dual GPU solution, the 4850 X2 is not frugal in its demands on your electricity bill. At idle our Core i7 test rig pulled 248W from the wall, which rose to 468W at full load. This is only marginally less than a 4870 X2 and far more than a single GPU card like the GeForce GTX 285 or Radeon 4890.

Sapphire provides a decent bundle with its card, with a suitable selection of TV-out cables and adaptor dongles as well as a full copy of 3DMark Vantage. You also get a Crossfire bridge connector should you want to combine two of these cards in Crossfire X, and the warranty is a respectable 2 years.

Overall the Sapphire HD 4850 X2 is a capable gaming video card, but its somewhat inconsistent performance at the highest settings makes it a less-solid choice than similarly priced single-GPU solutions. Cards like the GeForce GTX 275 and Radeon 4890 may not offer the same frame rates in less-demanding games, but their much larger texture addressing space makes them faster in the titles that actually require this sort of GPU grunt.

We therefore find it difficult to recommend this card and suggest you check out the 2GB variant instead, which will provide a much more predictable and fluid gaming experience even if it does cost considerably more.

This is an undoubtedly powerful gaming video card but a lack of memory holds it back at the highest levels of detail. It is also considerably louder and more power-hungry than competing single-GPU solutions that will offer more predicable performance overall.