1. No benefits in the serps with a .com over a .co.uk, although the .co.uk might have an edge if you're searching from the UK.
2. Initially the redirect might cause a loss of traffic while Google figures out what's going on. (They don't instantly figure out redirects and give your pages the same rankings.) Assuming you do a 301 redirect, you should eventually rebound.
3. Theoretically, the backlink benefits would still be there, assuming you do a 301 redirect.
There are obvious benefits to having the .com, but they're not SEO benefits.
|