Subdomain vs New Domain

I have two e-c0mmerce sites, Site A and Site B.

Site A Stats
PR6
Created 1998

Site B Stats
PR2
Created Jan 2010

Would it make sense to put site B as a subdomain of Site A to help increase rankings or leave it as a separate site?

I would leave it separate, because of the eggs/basket thing. If site A ever takes a hit for whatever reason, it will probably take the subdomains with it.

Thanks for the reply. The sites are both strictly white hat, so I don't really forsee a major hit coming to either site. Having said that, would putting site B as a subdomain under site A give site B an instant boost in the SERPS?

Actually I would expect a possible drop in serps while the SEs sort out the new location. Once everything is settled, the subdomain should inherit some authority and age from the root domain.

How much improvement depends on how much difference the authority and age will make vs. your competitors' current rankings.

for some of the real marquee terms, there are some high authority aged domains, but some of the less competitive terms (brand + keyword) are more easily attainable. i know theres no clear cut answer but i just have no experience with knowing how much of the authority and age the root will give off to the subdomain as Site A has solid age and authority

any other thoughts?

I have set up a domain 2 weeks ago with 5 subdomains which are all related to the same topic. The subs go in more deeper on one of the topics more deep than in the main domain. Well, you can ofcourse always add a few subdomains to BOTH domains for SEO.

I could have done it in the same main domain, but have done it this way, and I must tell that in Google I have seen several subdomains being ranked higher on certain keywords than the main domain. If it would have been different if I did it otherwise, I dunno, but I am happy with it. Btw, all done with WH-tech, cuz domain isnt that old.

PR does not pass to a subdomain. It will pass to a sub-page, but a subdomain is viewed like an entirely separate website from the root domain.