Yeah, alot of CV's are 4 ohms, but they're usually very efficient speakers, so not much power required (relatively) to make them play loud.
I would not exceed 7 speakers on the receiver.
And if you are running 7 speakers at loud volumes for extended periods of time, I highly recommend you drop $100-$200 on a used power amp of at least 50 watts/channel to relieve the receiver of some of this burden. Adcom, Rotel, NAD, AudioSource, AMC can be found fore cheap, and offer a lot of bang-for-the-buck. you could probably find a decent Carver, Adcom, Rotel etc 5-channel power amp for a good price too that would be much more capable of taking a beating.
So start saving them empty brown bottles and quit super-sizing your lunches for awhile, and lay off the receiver a bit...Better safe than sorry, nothing worse than frying a new new receiver.