I'm inclined towards a Gel; though, I've no insight into temperature range resilience. The fact that they can be laid on a side makes for potentially larger "glove" box. Locally a Gel cell battery can be had for near $90.
How about a Hawker Odessy, AGM battery. AGM-absorbed glass mat has the electrolyte in a glass wooll mat so it won't come out.
I have an Optima AGM in my welder and about 3 years ago a bud shot a hole through it with a .38. It still works fine with the hole clear through it. I don't believe Optima (Johnson Controls) makes a battery small enough for the R3 but Hawker does.
I have an 05 with a newer dealer installed battery and it is a little slow to crank sometimes especially when the engine is hot. I thought this might be due to engine compression, or maybe even battery cables being a little small to carry high enough start up amperage. To add to the startup amperage problem your lights, ignition, fuel system are all drawing at the same time.
Normally one would do a load or draw test on a battery. Can the same be performed on a bike battery? Can one use an automotive load cell tester
The ability of the battery to supply enough energy depends on the Cold Cranking Amps of the battery regardless of type and IMHO bike batteries have a minimum rating at best. If you find a good highly rated CCA battery please let us know.