Nuno Filipe
You talkin' to me?
In Reaper, your latency is ms is shown in the upper right hand corner, correct?
In a Profire 2626, the lowest buffer size is 64. I have a pretty powerful PC that was just built for me about 3 months ago and just yesterday I was trying to record guitars at 64 sample buffer and was getting crackles and popping. Sort bothered me as this thing SHOULD be able to handle it, and according to Reaper, I'm right around 3ms latency at 64 sample buffer (only running L1 on master and 4 instances of TSE 808, X50, LeCab, and EQ). If I set it higher to 128 samples, the problem is gone but I'm getting 4.3 ms latency. =/ It really isn't enough to throw me off though.
I might be wrong but the latency is due to your interface/drivers and not so much about the CPU power.
Edit: But of course you will need a lot of memory ram if you want to run plugins in real time.