I found this DSLReports news item from a year ago: »Comcast Shaking Up Speed Tiers (Again)
I think it still applies today. The speeds listed appear to be the continuous, non-PowerBoost ones.
"... Comcast is once again shifting their speeds around somewhat in DOCSIS 3.0 upgraded markets, all of which will eventually have these choices if they don't already:
Economy - 1.5 Mbps downstream, 384 kbps upstream
Economy Plus - 3 Mbps downstream, 768kbps upstream
Performance Starter - 6 Mbps downstream, 1 Mbps upstream
Performance - 15 Mbps downstream, 2 Mbps upstream
Blast - 25 Mbps downstream, 4 Mbps upstream
Extreme - 50 Mbps downstream, 10 Mbps upstream
Extreme 105 - 105 Mbps downstream, 20 Mbps upstream
Documents provided to Broadband Reports suggest Economy Plus is only a retention tier for users who call in complaining of high prices, and may not be available in all markets."