You can pull maybe 1.060, to 1.070 if your efficiency kicks ass, out of a 5 gallon mash-tun. Most I've gotten out of mashing in 5 gallons was 1.066 where I hit diminishing returns. So you can brew a lot of beers with 5 gallons, but you'd definitely be better suited with 10 gallons (unless you want to make higher gravity batches in smaller batch sizes).
Up Next: Saison, Tripel
Primary: Accidental Lambic
Secondary: Chili Pepper Smoked Porter(s)
Bottled: Brett B. Tripel, Dubbel, Robust Porter, Black IPA, Cal Common, Chinook/Vienna SMaSH, Kolsch, APA, ESB, Oatmeal Stout, Tafelbier