When ever I try a something heavy at V2 I noticed the bit rate on foobar shoots to 338kbps+ for 2 seconds?. Are they using a Bit reservoir as a work around for higher than 320kbps because much of the songs/albums size matches AAC/Vorbis at 384kbps.
It shoots when you seek in the track, thus it's a foobar bug. LAME is capped to 320 kbps by default because it's the limit of MPEG 1 Layer 3 standard.
Are they using a Bit reservoir as a work around for higher than 320kbps
Yes, LAME does that, on CBR 320 kbps as well. That doesn't affect foobar bitrate meter, it's dead 320 kbps all the time because all frames are 320 kbps, but the efficient bitrate may jump up to 450 kbps on transients. Typical MP3 behaviour.