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.