Ah, that's a bit different situation...in the OP you said you were down to 5BB which would have meant a chipstack of $3k at 300/600. That M value you're seeing is not Big Bets, though. That M value is calculated as:
Stack / ((#players*ante) + ((BB+SB)/2))
So 5357 / ((8*60) + ((300+600)/2)) = 5357 / (480+450) = 5357/930 = 5.76
Now, back to the hand. I know this is more discussion than your initial question, but we don't get much Razz analysis around here so I'm going to throw out some thoughts anyway. I'm definitely not a Razz expert (yet ), so my thinking analysis may be off a bit (but hey, that's why we discuss these things; so we can all improve).
Ok, the other factor I'm considering is that this is in fact a freeroll and freerolls
do play differently than even the lowest possible buy-in tourney.
On 3rd street, if you were going to limp with that hand and planned on calling a raise, why not just complete to start with? Take that initiative imo and show right off that you're looking to get your money in. That could help you slow the action some as well in case you're hoping to draw cheaply.
So, on 3rd, villian (massive stack) raises with a limper in front of him (you) knowing you're short. Obv either he's trying to scare you off a mediocre hand or he's legit...you'd have to give us a read on this if you have one about how he's playing. But it's fair to assume he's fairly legit. Even if we only give him one down card 9 or lower and the other purely random, based on the board we are a 2:1 dog here. This is why I like opening here instead of limping.
Anyway, 4th is obv really good for us in the grand scheme as our better hit makes this a near coinflip now as a 55:45 dog. But that 9 wasn't exactly a horrible card for him either, so I would possibly have checked now flat call his likely bet to see 5th then reevaluate. However, since mentally it seems we have committed to playing this out at this point, I don't necessarily hate jamming here either.
5th street again is a huge hit for us and makes about a 3:2 favorite now and jamming is correct here imo even though his cap is telling us he's now made his 9 low (which shouldn't be a surprise based on 3bet 4th str).
6th street puts us back at a 56:44 dog, but his lead is giving us 14:1 to call. But really, calling isn't an option at this point. We've dumped 2/3 of our stack into this hand already. If we flat and miss 7th, then we lost 80% of our chips are are pretty much screwed at that point. So we either suck it up and fold leaving us our 1/3 starting stack to work with or we raise like you did. In all honesty, based on everything else in this hand, I'm raising here like you did.
So of course with less than one BB left, even with 7th bricking, I can't see folding now. Sadly we only win here 1 out of 25 times (4% ish) so we're not even getting the right pot odds
to call blindly hoping for an utter no good bluff. But with M now down to 0.53 we're screwed either way. It's a freeroll; might as well toss those last chips in anyway.
Now, one other train of though I had going the other route real quick...limp/call 3rd. Check/call 4th. Check/call 5th. Check/fold 6th. This approach not only keeps us in the tourney, but also means we've only lost 1/4 of our stack that hand and have plenty of chips to play a bit longer looking for a better spot.
Anyway, that's my thoughts on this.