Best semi-recent RT and firmware?

I have been roasting calmly, with little drama for probably far too long, by avoiding updates. I’m currently on RT 2.5.5 and firmware 515; my Bullet is V1 with the IR sensor upgrade. Please nominate a combination of firmware and RoasTime that should give me little or no trouble.

So you essentially have a V1.5 Bullet which is what I have (though mine was delivered that way). I’m using f/w 540 and RT 2.5.5(.227)-stable without issue.

I have used the -alpha, -beta & -internal versions, but all three have an issue using the arrow buttons (upper right) to cycle thru the roasts (changes from °F to °C after the first chart while maintaining the °F label; it’s an error that was fixed but crept back in). Product versions .221 (-alpha), .222 (-beta) and .233 (-internal) are all larger files by 20 MB. Sorry, don’t recall what the extra size is for… maybe saving codes to Aillio server thrown during roasting… ??

Edit- just found f/w 553 (?? I think that’s right) which I installed but have not yet used to roast. I suspect comm has been improved as getting the Bullet initialized this time was much less troublesome.