Fitting a bike question

[Lbrava]

Hi Guys/Gals, new to emtb's & have a few questions on bike sizing. I'm coming off road bikes which have become to uncomfortable and don't think I can compare a medium road bike to a medium emtb. I'm probably buying online (a Luna) & trying to compare the Luna frame to Trek/Giant bike geometry. But I'm not sure what is a make or brake dimension. From what I've read they say reach & stack are important but I also think the effective top tube length is pretty important. The Giant site & Trek say I should be on there medium. At 5' 9" the Luna site says the same but do not have any mediums for sale. So looking at the Giant medium spec vs Luna small spec I see very minor differences in size.
The Reach on Giant M is only 3/8" longer than the Luna S - I can't see 3/8" affecting comfort ?
The Stack on Giant is 5/8" longer than the Luna - Seems the 5/8" could be adjusted with seat height ?
The Effective top tube length on Giant is only 3/8" longer - I can't see 3/8" affecting comfort ?
The Crank to seat post is 1" longer than the Luna - Could be adjusted with seat height ? The Wheel base on the Giant is 46 3/4" which is 1" shorter than the Luna
Am I stupid trying to talk myself into a Luna small frame bike ?
Would appreciate any & all feedback
Thanks

 

[dodgeman]

I’m not sure if this helps but I’m just over 6 feet tall, my wife is about 5’7”. We both have the same Trek Verve+3 bike but hers is a medium and mine is a large. When I ride hers I can get the seat high enough but the handle bars are noticeably closer to me. Not uncomfortable but it feels off. I’m not sure if it’s because it’s “wrong” for me or I’m just used to mine. At 5’9” tall it sure seems a medium would be correct and I’m not sure you would be uncomfortable on a large.

 

[CodyDog]

My wife is 5'9" and ride s a medium in a Specialized Como if that's of any reference. I'm 5'11' and ride a large.

 

[Lbrava]

That's a thought, I didn't consider going up to large frame. On road bikes with leaned over riding position I was uncomfortable due the longer reach of a large frame. With the upright sitting on emtb I guess it's a different ball game. I also know on emtb I'll be standing a lot more than on a road bike. I need to test ride a few unfortantly the bike shop is about a 3hr car ride.