To give a fair comparison of this CPU's baseline performance we started our testing by adding it to our current LGA1156 test board, the P55-based Intel DP55KG. We then ran our standard suite of CPU tests consisting of everyday CPU intensive tasks like editing photos, transcoding video, and gaming. We're currently still using Vista for our testing to make for easy comparison to passed results but we shall transition to Windows 7 from this point onwards.
For comparison we've included the Core i7 965, which was Intel's fastest CPU though it's just been replaced by the slightly higher clocked but otherwise identical 975, along with the Core i5 750 which is the cheapest true quad core, Nehalem-based CPU. We've also included two of Intel's higher end outgoing Core 2 range - the dual core E8500 and quad core Q9550. As for AMD's competition, we've looked at the Phenom II X4 965, which despite being AMD's fastest CPU is still cheaper than either the Core i5 750 or the 661.
Looking first at single-threaded applications and the combined advantage of Turbo Boost and the Core i5 661's high initial clock speed means this CPU is a very strong competitor. In our Photoshop image editing test it only lost out by four seconds (two per cent) to the Core i7 965 – a chip that costs about five times as much – and only missed out to the same chip by four per cent in our standard definition video encoding test. In the single threaded version mode of Cinebench it even took first place by a notable five per cent margin.
Understandably, when it came to multi-threaded tests the Core i5 661 didn't hold up so well. That said, it certainly left the Core 2 E8500 far behind and held its own against the Core i5 750, Core 2 Q9550, and Phenom 965 BE and it was only really the Core i7 965 with its ability to process eight threads at once that pulled away.
Looking next at power consumption and it's no surprise to see the Core i5 661 drawing significantly less power than those CPUs with more cores, at both idle and under load. Perhaps most interesting is just how much power the E8500 uses – it's worse than the Core i5 750 at idle and the same under load despite having half the number of cores. This really highlights the microarchitectural and manufacturing improvements between the Core 2 and Core i* ranges.
One of the apparent advantages of this relatively low power consumption is that it could leave plenty of headroom for overclocking and indeed that appeared to be the case in our testing. Without the slightest hassle we managed to up the Core i5 661's base clock speed to 4.05GHz without any extra voltage and we're sure you could easily push it a fair bit further without too much trouble. This improved its Cinebench scores from 3,967 and 9,133 to 4,442 and 10,262, respectively - a cool increase of 12 per cent across the board. Impressive though this is, the similarly priced Core i5 750 can also reach 4GHz and it has four physical cores.