Nitro's response was perfect - I know of a few platforms that are pretty darn fast without their risk - factor in their ~100-120ms risk check and you go down hill. Trade over Internet vs. FIX, etc. Hopefully you can see that the configuration and design of the overall system is more important than one generalization. I tell 9/10 traders that ask me to sell them a new machine that they already have adequate hardware - it just isn't setup properly. A question back to the OP - do you mean the lowest latency front end or do you mean the lowest latency matching engine?
I remember the good old days. A stack of Buy/Sell pads, a card to keep my positions on, calls on the left, puts on the right, my est. deltas on the top right and 5 new pencils every day. I'm like a dinosaur.
As has been mentioned I am worried about the lag time added by risk checks. I am looking for platforms which address this well, or at server side execution entirely (by which I mean risk checking on the same machine as the algo). This has to be addressed by the platform and the clearer. This is where I wonder how some common platforms, like TT, can have consistent performance across so many brokers as opposed to more custom specific setups with a given clearer. I prefer to be as "broker independent" as possible in case I need to expand in the future.