10 gallon tun, 2 x 5 gallon boils?

The mash tun is big enough to do 10 gallon batches, but I only have access to two 7 gallon boil pots. Any thoughts/suggestions on how and what to brew? I am thinking you could easily do different hop additions in the split boil, try different yeasts, but does anyone have experience with this kind of approach? What else could be changed in the boil and fermenter to make different beers with the same base wort?

Also, I only have one immersion chiller, which could be problematic and certainly slow. Is this a deal breaker?

Your first runnings could make a higher gravity beer.....you could do a 90 min boil on one of the batches, that would stagger them so you could cool one....

fpweeks had a good suggestion. An ESB might me nice. Fullers brewery makes one wort, first runnings make the ESB second runnings make the London's pride. (I think, don't quote me) I've been wanting to do that clone for awhile now.

Same grain profile but with different hops, boil times, yeast, fermentation time & temperatures will make all the difference.

Maybe try a double brew day w/ 5 gallons each pot and do one 60 minute boil of a lighter beer and the other do a 90 or 120 minute boil for a bigger beer. You could also use BK additions such as LME, DME, lactose. Also, if you were to want to make a dark & light beer you could use the immersion chiller to cool down one BK post-runoff to 150-160F and steep coursely ground chocolate malts (or other roasted malt) in the BK for 15-30 minutes using a few muslin bags. There is a lot you could do with that setup I think.