Given grade 2 ptosis, how common is it to receive good results with simply implants? (Photos)

From your photos you appear to be borderline for "needing" a lift. It is possiblethat larger implants could give you the breasts you desire with more volume and fullness but the breasts and nipples may stil have the same lower position on the chest wall and or there may be a snoopy breast ( ptosis off of the implants) and you may desire a lift in the future. Large implants only help up to a point, then make things look worse with residual ptosis.
If you want the best position and shape, you should strongly consider a lift after a consult with a Board Certified Plastic Surgeon who can review these options and likely outcomes based on your anatomy and tissue characteristics.

Hi Nububs; If implants are used alone without a breast lift when the nipple is lower than the infra-mammary crease, even with above muscle implants, they are going to be too low. In your photos, there also appears to be quite a long distance between the nipple and the top of the sternum and from the side view they look low on your arm. You also have glandular pseudo-ptosis. I recommend a formal consultation in order to give a definitive answer but it looks as if you will need a lift with your implants. Our Vectra 3D imager is wonderful of helping to illustrate what the results can look like with and without a breast lift. Low breasts look matronly and part of a cosmetic breast procedure is to look youthful! I don't like to place scars on breasts and in fact, do the TEAM breast augmentation, that hides the scar off of the breast, but the position of the breast on the chest and ideal relationship of the nipple and the breast mound give the best aesthetic results. We'd love to see you for a consultation. 

Patient concerns regarding the appearance of their breasts can typically be divided in two pools: volume, ptosis (droop). The procedures to address these issues are as different as the issues themselves. However, these concerns are not mutually exclusive (some want smaller less droopy breasts and others want larger less droopy breasts).
There are two factors which can help to answer the question of which surgery will deliver the most satisfying result: mastopexy, augmentation or both. Patients must first consider the position of the NAC (nipple areolar complex i.e. the pigmented portion of the breast) as it relates to the inframammary crease. If the nipples are at or below the level of the crease the patient may benefit from a lift or mastopexy. The breast lift is designed to elevate sagging breasts to a more youthful position. It also helps to reshape and tighten the skin of the breasts. This is typically accomplished via a periareolar (around the nipple) incision with or without a vertical incision.
Mastopexy is an effective way to address sagging breast, however, the changes which accompany weight loss or pregnancy can also decrease volume of the breasts. When a woman wants the volume restored, or increased, a breast augmentation will also be needed in conjunction with mastopexy. Augmentation can help restore the volume loss which is well known to women following children. There are a number of options available to women considering augmentation ranging from size and implant type to access incision.   
A breast augmentation alone may be appropriate if ptosis is mild. If the patient is comfortable with the natural appearance of the breasts but desires them to be larger, a breast augmentation alone is the right procedure.  Augmenting significantly ptotic or sagging breasts tends to magnify the problem. In these cases, a mastopexy performed in conjunction with an augmentation is preferred.
Based upon your photos, you would benefit from a formal lift in concert with an augmentation. You have glandular/pseudoptosis with a low grade of NAC ptosis. Without a lift, you run the risk of creating a "double bubble" with the breast mound hanging off the implant.
As always, discuss your concerns with a board certified plastic surgeon (ABPS).