The single-core Geekbench scores for the I5 vs the I7 can be attributed to the 12% higher Turbo Boost speed of the I7, 4.1GHz vs 4.6GHz. The multi-cored scores seems to mostly reflect the higher Turbo Boost clock with only a very small benefit from Hyper Threading. (insert usual disclaimer about the artificially of synthetic bench marks)But I’m not sure whether to get the i5 or the i7.
As others have mentioned, the I7 does open you up to hyper-threading exploits (although this is extremely unlikely)