the BRCA/EFRA rules were designed for lipo, sure the EFRA dimensions of lipo's are slightly different than ROAR but there are plenty of 5000+ mah batteries on the approved list.
i need to add almost 100g to my T3 to make 1425g with a 5200 50C battery. I'm sure the majority of other cars can make the weight otherwise they wouldn't make the rule.