Unfortunately there isn't a uniform standard for mats so R5 from one manufacturer could be R7 or R4 from another.

One mat that seems to get mostly positive comments about the given rating is the Exped DM7, now available in a UL versiopn at about 23 oz inc pump.
(it's a down mat)
Another one that many have compared to the Exped is the Therm A Rest X Therm,15 oz, rated at R5.7.
(the warmest of the Neo Air family)