I was texturing an outfit.
The texture was 500x500 px which was great for details, but the template that I was using was 1500x1500 px. 
I, of course resized the texture to keep the pattern small, but when I tested in DAZ, I lost some of the needed details of the pattern (It was lace). To work around this problem, I instead resized the template to 5000x5000 px. I got the results that I wanted.

I was just wondering if there was a way (or ratio) to make beautiful textures that are high resolutions smaller without losing details in 3D. I don't nessarily want to resize my templates so big just to get the results that I want. 

Any help or advice would be much appreciated.

There is a way, but it requires modeling the lace, which, would actually use more memory than texturing.

500X500 is definitely too small for a quality texture, but 5000X5000 may be a bit too big...  Somewhere around 3000X3000 should give you good results, that's about the size of texture most merchants use, it depends on the figure you're making the texture for a bit...  For example, 3000X4000 would be a good size for the texture of Aiko3's body, but that size would be too big for Aiko's eye texture since Aiko's eyes are much smaller then Aiko's body.  For the eyes it would be between 500 to 1000.  To give you an idea, look at the size of textures you consider of good quality for the same outfit, it may help you decide which size to make yours.  Remember to keep the proportion when resizing your template though.

Thanks, I guess I'll just have to fiddle around with sizing.

I don't know if this applys to your specific needs, but if you are manipulating the texture such as filling in adjacent areas, rotating etc. Try working at the highest resolution your machine can handle and at 16 bit. This will maintain as much data as possible. Avoid cloning as much as possible, instead copy and paste the area you want to expand and use the erase tool to blend with the underlying layer if needed. The healing brush works well for small areas. Anytime you manipulate pixels in any way you degrade them to a certain extent. If you you need to resize an area use the measure tool to determine the finished size you need and resample the texture area as opposed to using the scale or transform tool. When the entire map is finished resample it back down to the size you want and convert back to 8 bit. Bump maps will certainly help to define a texture. Another technique I use that seems to make textures really pop out is to place a duplicate map that has been treated with the color photo filter of your choosing and you might try adjusting levels of this secondary map. Place this map into the translucent node and experiment with different percentages between the diffuse and translucent map.
Chris