No one thinks the performance problems are implausible. But hardware can only do so much to make up for the worst excesses of antivirus. Behavioral scanning doesn't require huge amounts of memory and has negligible need to touch the hard drive. On-access scanning by definition barely needs to increase the number of I/O operations. It shouldn't bottleneck the machine if it's done competently. So then you're just loading outlook off a hard drive, which took several seconds the last time I tried it.