Unfortunately, the last I checked, the Kelty White Cloud does not come in an x-small size. A friend had one and I really wanted one too, but I am too small.
The major part of a pack's weight is the internal (or external) frame and suspension system, hip belt and shoulder straps. The actual "bag" is a smaller part of the total weight. Thus, increasing volume does not proportionally increase the total pack weight. The only problem I see with a too large pack is that you will tend to just add more because you can!
Regardless of volume, the pack has to be able to carry the weight. The most important thing is to get a pack that FITS best and has the weight capacity needed. Once these criteria are met, you can play with volume. I find that the stated "weight capacity" is often too optimistic. For me if a pack is rated at 45 pounds, 35 is really my "comfort" limit.
You also have to pay attention to the design proportions (where does the pack get its volume). I bought a pack once that had much of its advertised volume as an expandable top. When loaded, it was very unstable and top-heavy for the x-small frame. It now is relegated to a travel pack (luggage). Some packs use extra width go gain extra volume. Be careful here - the pack can restrict arm movement when using trekking poles. Other packs get the extra volume by being deeper (front to back). The closer to your back the weight is, the easier it is to carry. Some packs have much of their "volume" in tons of small pockets, which often are too small to be useful. I have had two packs, listed as the exact same volume, and one works fine with all my equipment; the other does not.
Because of the above, I am still a proponent of getting equipment first, then fitting it in a pack, and then be sure to carry it around a while to see if it is comfortable and well balanced for your body. As you gain experience, you can begin to reduce volume and weight of your equipment and learn what is really needed and what is not. Maybe after a few years you can get by with a smaller pack.
After nearly 50 years backpacking I am still experimenting, deleting, adding, trying UL gear, buying different packs. If you watch out for sales, packs really are not that expensive (for example, compared to sleeping bags or tents). If I buy a pack and it does not work well after a season's use, I simply donate it to my local boy scouts.
One pack I will never give away is my original 1968 Kelty external frame with extension bar. I still occasionally use it. But now that I am no longer lugging 30 pounds of technical climbing gear, it is a bit over-kill.