Yes, it's completely normal. Aluminum is a conductor so it will feel hot, even if the innards are not hotter than normally. Slow downs are most likely caused by something else.
Describing "feeling" of the temps without numerical numbers is very subjective. re: It might feel hot to some but its very hot to others. To eliminate subjective feelings (of wind venting out of your iMac), do install iStat Nano (from iSlayer). Its a free Widget that shows the inside temps. IMO, the inside temps is what folks need to focus on. URL is: http://islayer.net/apps/istatnano/
Install iStat Nano, under "usual load" operate your iMac for a 30 minutes, then tell us its exact iStat Nano numbers. iStat Nano can show current fan RPM speeds as well.
If wondering, the iStat Nano "inside temp" numbers of my iMac are: