I was wondering if i could install some 4.5" RE lift springs and put off on the CYE kit for a while and be fine with driving mainly on road for the next few months.

From what i hear it's the bad vibrations you get from the steep angle in the rear drive shaft. Some jeeps are worse than others so you could get lucky, but then again it could shake like crazy. The way my jeep already goes through U-joints in the rear drive shaft i would bet you would go through a couple in the few months you plan on driving it like that. im no expert so im sure someone that has done it can help you out more than me.

I ran mine for a few weeks before I did the CV/CYE kit and it was horrible.
I planned to do it the next weekend and had to run for two - hated every minute until I got the CV/SYE kit in. Then later I dumped the tcase and got
an Atlas II and got another six inches in length - and I still needed
the CV ...

DID YOU HAVE THE TRANSFER CASE DROP INSTALLED BEFORE THE SYE.

No - I wanted the CV so I did not put the drop in - that is important.
I needed the clearance. Later I went to the RE long arm - after breaking the short arm in a roll. I got the CV and SYE in the RE kit so
I did not plan on the drop . Put a 1 BL and MML in also.

so you think that I'll be fine as long as i put the transfer case drop on ?

If you put the drop in you have a much better chance of being OK - with the drive line - but the stock belly plate can hang up if you are rock crawling - so it is a trade off.

Every jeep and every lift has it's differences - because everyone has different trade offs that they are making - out here in the land of rocks, sticks, thorns , and stings every inch can mean
the difference between driving home - or walking.

You have to have a feel - vibration - for what the stock setup was - used as a baseline - and what amount of vibration you are getting with your setup. Its easy diagnose a problem wrong if you have not seen and heard a few rigs.

When I installed my RE 3.5" lift on my '03, I had bad vibes, I installed the Tcase drop, and still had some vibes...the 4.5" springs are taller then advertised, the chances of you not having some vibrations without the SYE are pretty slim IMHO.

if i get bad vibes outta the driveline could i drop the transfer case a bit more to delay the SYE as long as possible

I always considered the tcase drop to be a BAD fix. Everything I ever did was to get the thing up
and then gone ...

I found the CV and SYE were worth the money. The RE guys recommended that I switch to the Atlas II because it gave me back six more inches.

Hey BAB-IE look at that !!!

In the end it will not cost you anything to put a few more spacers in the drop and SEE . But you are going to burn alot of time tweeking the axle angle to be sure that you got it right.

Case in point - when I was getting close to a really noticeable vibe problem - I would get situations where the angle of the axle was so close that I would get vibes when I coasted down hill - but not when I was under power - going up the same hill.

I burned enough time doing that to know it was just worth the money to do the SYE and get it right - and get it done.

In my case I had the Long Arm in with the flat belly plate and I could not get the RE supplied transmission mount in - without vibes - I finally had to make my own - to get the angle right.