I'm soon going to be stuck for a while ... I am currently still on E72. My metric centuries (62 miles) and 'long' metric centuries are usually less than 72 miles so they don't help. If I am going to do a ride longer than 72 miles, I'd usually think about making it 100 to count towards my lifetime goal of E100. The problem is that it is really hilly round here so either I do very hard centuries, or the same limited choice of flatter routes, or I have to travel quite a long distance to do those centuries - e.g. the Llandudno, (extended) Scarborough, Cheshire, or Humber Bridge forum rides
I need 4 x 73 miles for E73, 7 x 74 miles for E74, and 10 x 75 miles for E75. I'll try to avoid doing too many 76-99 mile rides because it will take me the rest of my life to achieve E100 if I do! I need another 58 x 100+ miles but only did 7 such rides last year. At that rate it would take me another 8+ years and I am rapidly heading towards 63 years of age. I'd like to think that I will still be riding centuries in my 70s but I'd prefer to achieve my goal before my 60s are over!