Ah, the roll vs. stuff debate! I have tried both methods and, frankly, haven't noticed any difference in wear on several different tents. Others may differ. Stuffing is easier, but I never realized until about 7 years ago that most tents don't have to be folded and rolled!

Re the original stuff sack vs. compression sack. First, set up your tent in the back yard. This is something you should do anyway; practice setting it up and taking it down a number of times until you can do it without referencing the instructions. After dark on a wet, cold, windy night is not the time to be learning! It's also a good idea to use the garden hose on the tent to be sure there are no leaks, something else you don't want to find out in the backcountry on a dark and stormy night! (That assumes a convenient hard rain doesn't come along while you're testing the tent, which rarely happens. :D) Anyway, after you've done this, you may find that when wet and cold, the tent will be hard to fit into the currently loose stuff sack! Glenn's idea of a separate sack for the fly is a good one. Be sure the tent is clean and thoroughly dry before you store it between trips, and consider a larger sack (maybe a large pillowcase?) for storage.

I presume you noticed that your REI tent is a 2-person tent while the SMD Skyscape is a 1-person tent. That's a big part of the weight difference. If you look carefully at the specifications and the website diagrams for the Skyscape, you should be able to do a mockup of the same dimensions on your floor with masking tape and string to see if the smaller tent works for you. (Not my idea, but Franco's; he's a frequent poster here who is also the Australian representative for Tarptent.) The Skyscape won't work, though, if you plan to share the tent with someone else!

SMD is a reputable firm (I've dealt with them a number of times; great customer service) and the Skyscape, while a new model, has received a lot of favorable comments. (I haven't investigated it because I found out the hard way several years ago that with my 75-lb. dog in the tent with me, a solo shelter is a bit too small.) I noticed that both the PU-coated nylon (Scout) and the lighter silnylon (Trekker) models are on sale through January 2.

On your pack: Will it compress (squish) down small enough so that it will be firm with a smaller (i.e. overnight) load? (That's what those outside vertical and horizontal straps are for.) If so, you can use the 55L pack for smaller loads, too. It's a handsome looking pack! Of course the most important feature of a pack is that it be comfortable for you with all your gear inside as you are hiking along the trail!
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey