I'm no expert but from what I've read a higher sensitivity speaker is better for a low power amp like the Cross Countrys. An efficiency or sensitivity rating tells you how effectively a speaker converts power into sound. The higher the number, the more efficient the speaker and the louder it will play with the same input power. An efficient speaker helps you maximize your available power. Most sensitivity ratings measure the speaker's output with 1 watt of input, 1 meter from the speaker. Some speakers' sensitivity is measured with 2.83 volts of input, instead of 1 watt. Since the stock Cross Country amp is low power get a higher sensitivity.
Alpine SPS-510 $55
Sensitivity 87 dB
Frequency Response 80 - 22000 Hz
Impedance (Per Voice Coil) 4 ohms
Top-Mount Depth 2"
Tweeter Composition: Silk
Woofer Composition: Polymer/Mica Composite
Woofer Surround: Rubber
Polk DB-522 $63
- Polypropylene UV tolerant cone
- Waterproof inner and outer surround
- 0.75" shallow tweeter design
- Top-mount Depth: 1.74"
- Cutout Dimensions: 4.76"
- 4 ohms impedance
- Frequency Response: 55-22,000 Hz
- Sensitivity: 91
Polk DB-521 $80
Driver Complement Mid / Woofer - Type Dynamic Balance driver with polymer/mica composite cone with rubber surround
Driver Complement Tweeter - Diameter 3/4 (1.91cm) "
Driver Complement Tweeter - Quantity 1
Driver Complement Tweeter - Type Silk dome
Electrical - Efficiency 93 dB
Electrical - Nominal Impedance 4 ohms
Electrical - Total Frequency Response 60Hz-22kHz
Electrical Power Handling - Continuous 45 watts
Marine Certified
Polk DXi521 $70
Tweeter Composition: Aluminum
Woofer Composition: Dynamic Balanced polypropylene
Woofer Surround: Butyl Rubber
Peak Power Handling: 135 watts
RMS Power Handling: 45 watts
Sensitivity: 93 dB
Frequency Response: 60 - 22000 Hz
Impedance (Per Voice Coil): 4 ohms
I like the specs on Cerwin Vega H452 BUT haven't tried them. $40
Mica-injected Reinforced Polypropylene Cone with Oversized Rubber Surround
* Linear Woven Treated Red Spider
* Power Handling: 35W / 250W.
* Woofer / Tweeter (in.,mm) 5.25" /1.0 (25.4mm).
* Mounting Depth: 1.850" (47mm).
* Frequency Response: 75Hz-18Khz +/-3dB.
* Sensitivity: 93dB.