Asda have 800gsm terry towelling towels nappies for those who're interested.
Elegant Living Bath Textile Range - White | Towels | ASDA direct
a comparison with Dunelm's 650gsm (approx), with Asda's on the left:
hard to compare, thickness-wise, given the difference in nap, and i'm still evaluating their absorbancy (hampered by hot, hot weather; Flaming June, no less).
but, they're cheap enough for anyone to buy and try.